Lightning on masts

Discussion in 'Boat Design' started by Fanie, Oct 28, 2007.

  1. PAR
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    PAR Yacht Designer/Builder

    The National Agricultural Safety Database out of the U of F

    MLP Inc.

    Ewen Thomson's excellent work

    ABYC recommends 4 gauge copper (tined) to the mast head on composite or wooden masts. 6 gauge bonding to all major metal components (tanks, engine, etc.) Air gaps, rods, all the exspected stuff.

    There are others, but these will put a search on the right path to ground (couldn't resist Tom).
  2. tom28571
    Joined: Dec 2001
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    tom28571 Senior Member

    Fair enough. These are some of the only reasonable approaches I have seen for lightning protection. There is so much snake oil out there, I did not know what you were referring to. These people do seem to avoid any sharp bends and keep the grounding conductors away from the hull sides which can cause a blowout to water through the hull. Just connecting the various metal parts of the boat to ground is not good enough.

    Actually finding a reasonable path to lead the conductors to ground while following the right procedure can be a real problem on a lot of boats though.

    Then, there is the bottle brushes and their claims which I question. There is also the claims made for the sintered porus copper grounding bars which are bogus.
  3. TerryKing
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    TerryKing On The Water SOON

    Alternate ways to find this information

    Agreed! Bluntly a lot of discussions about Lightning border on the FolkTale, including those on BoatDesign. Everyone, Please read those pages first!

    I had a LOT of trouble getting to those pages for some reason. I had to go through a weird proxy combination. Maybe it's subversive here in Communist China where I live? Here are alternatives in case you have problems.

    First, try directly. If that doesn't work,

    Overview of the problem and possible solutions:

    Technical Paper on Grounding Concepts for Lightning and Boats:

    Sometime, Someone should add a section on this on the WIKI under "Electrical Systems". If you're reading this, maybe YOU!
  4. Fanie
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    Fanie Fanie

    I didn't know there was whites it the Congo any more :D But they do have the goliath tiger fish there. Gets to be over 80kg in weight. Someone told me it's like getting hooked into a passing freight train at speed.
  5. lazeyjack

    lazeyjack Guest

    Lightning Strike

    This is a copy of the article published in Yachting Monthly

    My wife, Monique, and I had traveled the Intracoastal Waterway from Key West to Norfolk, Virginia, in our Moody 36, - Bambola Quatre, then cruised Chesapeake Bay, up the Potomac River to Washington DC. From the mouth of the Potomac to Washington took two and a half days. Once under the final bridge (with 2ft to spare above the vhf antenna), we anchored near a metro station five minutes from the center of Washington.

    After three wonderful weeks being tourists I had to return to the UK for a short time so decided to leave the boat in a cheap and safe marina not far from Baltimore Airport. We needed to get back under the bridge at dead Low Water so I started the engine and switched on my handheld VHF in order to communicate with commercial shipping. Then the US Coast Guard issued a storm warning, advising all boats in the Washington area to seek shelter so I dropped the hook again.

    I stood in the cockpit in the pouring rain, bare feet, in shorts and T shirt with water splashing around my ankles counting the sound of thunder claps. They were some 4 seconds apart, then 3 then two. Within five minutes the wind piped up and even in the sheltered anchorage it gusted to 45 knots. Just as suddenly it dropped the thunder claps were only a second apart and then there was an explosive bang: Like a huge artillery piece going off. A giant thunderclap directly overhead.

    Monique screamed.

    Drenching rain reduced visibility to a few yards and I saw plastic debris falling on to the deck. The wind came up again quickly to around gale force and went round 180°. The anchor started to drag.

    I motored into the wind to take the strain off the anchor and keep us from the very nearby lee shore. The engine alarm went off and I saw it was overheating. Shutting it down and running forward, I threw the second anchor into the water and paid out chain and warp. We stopped about 6 metres from a concrete wall.

    I went below to find out why the engine had overheated and I heard the little domestic radio receiving VHF transmissions -which it was not supposed to do. Then it died.

    Monique, who really does not like boats or cruising, asked if it was normal for her hair to stand on end? I did not realise she was speaking literally.

    The main VHF glowed for a moment, then died. The SSB had switched itself on but the display was blank. That was when I realised our yacht had taken a direct lightning hit.

    On deck again I found the wind instruments were all out and the masthead was bare. The VHF antenna and wind direction/speed unit were gone; lying beside the cockpit were the remains of the Hawk wind indicator.

    People watching from the marina said a fireball had hovered around our masthead. It had been a severe strike. We were lucky to be alive.

    In the engine room, investigating the overheating problem, I decided that the thermostat must have failed. With the nuts removed I found that the steel engine bolts had frozen themselves on to the alloy thermostat housing.

    Close examination showed a core plug had cracked and was blown half out of the manifold. I was definitely not going to move the boat that day.

    We went ashore and I e-mailed the information to Pantaenius, my insurance company. I also e-mailed an order to ASAP for a core plug and thermostat housing.

    Next morning I spoke to Mike, the Pantaeneus Claims Manager, who was considerate and very helpful. His advice: find a suitable marine electronics yard to do the repairs -possibly in Annapolis - and he would authorise them and send a surveyor.

    He warned me to be careful moving the boat as occasionally lightning strikes damage the skin fittings and allows a major ingress of water.

    I called ASAP to confirm that the order was on its way and found that it wasn't - I'd asked for it to be sent FedEx and at £30 to ship it (the order was only worth £ 12) they had considered it too expensive. I told them it was essential to have the part by Friday. I then went to find Bill, the excellent local mechanic, who said he would try to find a suitable core plug locally.

    Tuesday dawned and I discovered the 'house' batteries were going flat. The battery control system was out. The multimeter showed that there was nothing coming out of the solar panel at midday and the wind generator refused to function. We now had no engine, no solar or wind power and some shorts in the system were pulling the house batteries down.

    To my horror I found that, because it was late June, all the repair facilities in Annapolis and Baltimore were at full stretch. Then 1 was recommended to a company in Cambridge. Maryland, called Mid-Shore Electronics .The owner Marty, said that if I could get to Cambridge, on the eastern side of Bay. by the weekend, they could haul me out on Monday.

    Mike at Pantaeneus told me he would arrange for a surveyor lo be there on Monday. I called ASAP to be told that FedEx had not been able to guarantee the core plug delivery by Friday so the order had not been dispatched in case it was too late -but I would get it on Monday next.

    Bill, the local mechanic, found that no local US core plugs fitted my block so he would try to get one engineered.

    It was very hot and the house batteries were very flat. I was keeping my finger crossed that the engine battery would have enough power to let me start up. Then I realised I didn't have an echo sounder. The Potomac and frequently the Chesapeake are very shallow with anchorages that your creep into with just inches below your keel.

    Bill drove me 10 miles to West Marine where I purchased a Fishfinder echo sounder: it would have been almost impossible to motor-sail the 150 miles from to Cambridge, including overnight anchoring without it.

    Monday dawned but the FedEx parcel did not. However, on Tuesday at 1000 the delivery happened and by 1100 the engine was assembled. By 1130 we were u under way - and no longer concerned with the low bridge as Bambola’s mast height had been reduced by the loss of the VHF antenna by 3ft.

    After two days of motor sailing we entered the Choplack River, arriving at the yard in Cambridge, Maryland 10 minutes after it closed for the weekend.

    Marty from Mid-Shore Electronics arrived on Monday and went through the boat with me - virtually every electrical item had been damaged. I had installed almost every bit of the electronic equipment myself and it was painful to see the results of so much time and effort destroyed.

    Charles, the Pantaenius-appointed surveyor, arrived.

    Bambola Quatre was hauled, Marty was authorised to carry out the work and Pantaeneus transferred a deposit. The final cost to Pantaeneus was $37.000 (about £23.000). II cost me almost four months' cruising and my deductible £1,000, plus 30% of the cost of the new radar and VHF which were both more than 10 years old. Incidental costs such as air fares, car hire and phone calls have added around another£1.000.

    I was lucky that everything in the boat was properly bonded to keel bolts, Dyna plate, sacrificial anodes and prop shaft.

    My mast support is stainless and bonded to keel bolts in the hull. There was a lot of discoloration between the foot of the mast and the deck plate. I recently delivered a brand new boat – a Bavaria - to the Mediterranean and was surprised to see that the bonding of the electronics was non-existent.
  6. SeerAtlas
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    SeerAtlas Junior Member

    Lightning strike

    Question, Was your mast taller than the other boats around you?
    BTW, every strike on a yacht I've heard of resulted in masthead fittings either 'disappearing' or raining to the deck in pieces. If nothing else, this indicates to me that the *highest point* proposition has some validity.

    As for metal vs. other substances..I've got a small ranch that encompasses a 3 or 400 foot high hill about a quarter mile from the gate which is low in the valley. I had just let go of the gate, my hands probably a foot from it, when it was struck by lightning. It blew me off my feet and back about ten feet, and may have knocked me out for a few seconds. This area was surrounded by trees 30 to 40 feet higher than that gate for miles in all directions, yet it went for the metal.

    Put these two together and just off hand, it seems to me, that those with wood (dry) :) or fibreglass masts without a lot of cabling or steel on them are likely to fare better than the guys near them with steel or aluminum masts. I'll have to find some scientific studies on this, but running a thick steel or copper cable up that wood or fibreglass mast might amount to setting out the doormat and crying "HIT ME" .

    I'd be interested in seeing reports from the pre-steamship era on the lightning damage to wooden ships at sea.

  7. SeerAtlas
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    SeerAtlas Junior Member

  8. longliner45
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    longliner45 Senior Member

    ok fellas ..I am not a rocket scientist ,,I am a power lineman,I see and deal with lighting strikes all the time,,,what I find is ,,it damages equipt and goes into the house ,via ,your service ,,it does,, but rarely blow the top of the pole off,I have seen damage to fishing boats made of wood,,,bows splinterd as she was broaching a wave .,one thing I would like to clarify ,is electricity is always trying to find a way to ground,so I dont buy the photos of lighting reaching up from the ground ,,,now with that said .(question)if you have a wooden boat,,and a aulminium mast,,which should be inuslated,from ground.via wood ,are you ok? ,,it is not called electrical theory because we know all ,,it is called theory because of variances..dirt will tract,wet wood will tract and so on,,,,,,my asumption is that since you are on a boat ,,you are a delta system,supplying your own ground ... but at least while you are tied up at the dock ,,and not there to oversee,you could take some precautions,likegrounding your boat with number2 copper,to a stake in the ground or systems nuetral,but off shore you will be on your own,,and also if you done the latter ,,,what about electrallisis?,,,,basically Im asking the old salts here....also if you look at every power pole ,,you will see a number 6 copper ground wire
  9. PAR
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    PAR Yacht Designer/Builder

    A lightening strike is just like picking the number for the local lottery, the odds are the same regardless of how close they've come before. The average ranges from 400,00 to 600,000:1 odds you'll get a spike close enough to seriously harm you. It may increase or decrease your odds slightly, if you're the highest or lowest thing around, but the strike is reasonably random in nature, so most folks can feel pretty luckily, if a bit scared in a storm. It can hit a ball player on the mound, while missing the stadium towering around him. It can hit a golfer (whether he's in mid swing or not) in spite of 50' trees on each side of the fairway. It's random, though being on the water with a metal stick jutting skyward is increasing your odds (but not by as much as you'd think), it's still random occurrences. Protect you're boat, avoid nasty weather when you can and you'll likely be one of the 99% of the boating public that doesn't have an issue in their life time.
  10. longliner45
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    longliner45 Senior Member

    thanks for calming the quell par,, but also,,lightening does strike twice,on many of our circuits we know were to go from past strikes,,,and most of the time it is the same ,,lightening,,as you said it is random.for some reasons it repeats and others it is just one time ,,I think I will pass on putting a bunch of money and time in prevention ,,,,,just me ,,It is probably better for me to worrie about drunk boaters and electrallisis ,,,longliner
  11. Ike
    Joined: Apr 2006
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    Ike Senior Member

    I just got my October issue of Technical Information Exchange, put out by BoatUS primarily for Marine Surveyors and Investigators, but a really interesting read for designers and builders. You have to subscribe to read it on-line as well.
    Anyway, in this issue there is a very good article by Ewen Thompson on lightning protect that takes a whole new approach. It is essentially protecting boats the same way buildings are protected on shore. He proposes using multiple air terminals around the periphery of the boat with multiple external conductors on the outside of the boat, terminating at a grounding loop at or near the waterline, that goes all the way around the boat. I wish this article were online for all to read but they haven't put it on the BoatUS Web site yet and I wasn't able to find it anywhere else on line. The U of Florida web site on lightning say Ewen Thompson no longer works there all though they have his web site up. His new web site is A synopsis of the history of lightning protection is at and near the end of the page he goes into using multiple air terminals and side conductors.
  12. Man Overboard
    Joined: Oct 2006
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    Man Overboard Tom Fugate

    In my studies, I have read a book that may offer an explanation for some of the questions raised in this post

    Quote by Chandler
    The following explanation is presented by Kasemir and reiterated by Lars Wåhlin in his book "ATMOSPHERIC ELECTROSTATICS" page 64

    Kasemir (1950b) who believes that the mechanism involved is that of induction. For example, consider a negative charge centre in the lower portion of a cloud (see Fig. 27a.) from which a leader stroke has just reached ground. Not much charge is brought down because the negative charge in the cloud is bound on small drops or precipitation particles. On the other hand the earth's surface, which is a good conductor, can easily supply positive charge up to the cloud through the ionized channel provided by the stepped leader. When the positive charge in the return stroke reaches the cloud it will penetrate the charge centre like a giant lightning rod which causes the cloud potential to drop drastically since many field lines now are much shorter (see Fig. 27b).

    A Historical perspective appears on page 12:
    It was B.F.J. Schonland and his team in South Africa who discovered the different sequences of a lightning flash with the aid of a Boys camera (Fig. 6) and revealed the initial process of the stepped leader. Boys' pictures show that a bright-tipped leader works its way down from the Fig. 6 Boys’ camera photograph of cloud to ground discharge. cloud in steps. When the leader gets near ground it is met by the main return stroke which carries the main discharge current through the ionized conducting path provided by the leader. Normally the stepped leader is invisible to the naked eye and only the main stroke can be seen. The return stroke therefore, appears to start from ground explaining the saying that lightning travels from ground up.

    Peter does a good job of explaining this in plain terms in post #18

    Going back to Fannies original question:

    Wahlin offers an explanation that counters the rationalization that a lightning rod (or mast) attracts lightning:

    page 67
    Modern lightning research has proved that the function of a lightning rod is not necessarily to attract lightning and lead it to ground in order to dissipate its power. Careful studies show that large amount of corona discharges occur at the point of a lightning rod before lightning strikes. The corona discharges produce numerous ions which often develop a protective dome around structures fitted with lightning rods. A large conductive dome or sphere has a smoothing effect over protruding surfaces and will lower the electric field strength in its vicinity. Experiments by Vonnegut and Moore have shown that a conducting wire supported between two mountain tops did not get struck by lightning as often as the mountain sides. In fact, the lightning seemed to avoid the wire which can be explained by the above effect that corona must produce a large diameter ion cloud around wire. This has the effect of lowering the field strength in its vicinity.

    Quote by Seer
    Whalins explanation explains why more boats (especially sailboats) aren’t struck by lightning. (at least those that have metal masts)

    Corona discharge is of course not foolproof, boats still get struck by lightning; the lightning protection system adds some protection for boats that are struck.

    A through reading of the entire text will prove worthwhile for those interested. It can be found online here:

  13. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Thanks everyone for your replies, some of youry went to some lengths, double thanks, I now know a little more about lighning and what to expect on a boat.

    From a practical viewpoint, I am not going to worry about special wires or strips. If the lightning is going to strike the boat, there's not much you can do about it any way, and the precautionary steps may or may not work.

    Since there are thousands and thousands of boats with masts in storms every single day, it seems the amount of fatal strikes are really very low, as someone suggested kinda like winning the lottery (yeah right).

    Seems the thing to do when a storm is up, check the anchor, fire the kettle up, sharpen some hooks, or read multi-hull magazine ;)
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